> No, the problem is that this spoofing is a minor problem and any
solution is easily evaded by spammers.
Please explain how. I think as an exercise it would be instructive to give an
example of how a spoofing solution would be evaded (easily). I agree that
You keep a variety of name servers around the net. You register a
new domain every day (or week, or however often you need to avoid
blocking). And each day you send authorized email "from" the new
domain, using an authorization server that allows mail from any IP
address.